Lab 1 - System Wiring

To wire an advanced control system and write combinatorial ladder logic programs.

Electrical Description:

This lab will involve wiring 115Vac from a building supply. Some special items must be noted.

1. DO NOT CONNECT THE SYSTEM UNTIL all wires have been connected and checked.

2. Make sure the ground is connected to all devices.These are typically color coded as green, or have a ground symbol. Note: power should not flow through the ground, it is only for emergencies to draw current out of the cases of electrical equipment, and into the ground beneath the building. In other words the ground and common are not the same thing.

3. Normally the AC has 2 wires (for a single phase). For consumer applications we need to make sure the polarity is correct, so that the ‘hot’ (black) wire is switched off, making electrical shocks less likely. Note: in reality, even if these wires are backwards the power will still be delivered to the load.

4. After connecting the power to the devices, it is a good idea to plug them in and check operation before proceeding to connecting other devices.

5. Try not to daisy chain power connections (like a string of christmas lights), but connect the power cord to a terminal strip (power bus), and then connect to each device to the terminal strip. (see the figure)

6. Do not leave loose, or exposed wires. These will only lead to short circuits, electric shocks, or other problems. Tighten the wires. If doing this for permanent jobs, the wire should also wrap around the screw. Note: leads with banana plugs or ALIGATOR CLIPS ARE PARTICULARLY PRONE TO CREATING SHORT CIRCUITS.

Inputs and outputs also require a few notes:

1. A PLC rarely has an internal power supply for inputs or outputs. You must always connect an external power supply for inputs or outputs.

2. The ground and common are terms that are badly confused/misused. A true ground is an electrical connection to the ground beneath a building that will draw away current if there is an electrical fault. A common is a reference voltage for all parts of a circuit, typically 0V. When connecting devices such as sensors and actuators we want to connect them to a common. This problem is normally overlooked, but when we have systems with mixed power sources (eg. 115Vac, low voltage DC) we must separate these. Do not connect the common to the ground. BE WARNED, many low voltage devices (such as power supplies, sensors, etc.) show the common as a ground.

3. Remember for relay outputs there is no common, the output is just a switch.

The system is wired to include an estop that will cut the power to the outputs, but allow the plc and inputs to continue working.

The sourcing and sinking sensors to be used for the lab are shown with their conventional systems, as shown below.

Pre-Lab (Done individually)(NOTE: These, and all other Pre-labs will be checked before every lab. A mark of zero will be assigned when prelab materials have not been completed before the start of the laboratory):

1. Review the manuals for the input and output modules for the Flex-IO modules.

2. Prepare a wiring diagram using software. AS A MINIMUN, the wiring diagram should contain the following elements.

- 3 PNP proximity sensors

- 2 AC proximity sensors

- start and Estop inputs to disconnect outputs

- 3 solenoid outputs for pneumatics

- 2 output lights

- a power supply and requirements for various

- all required safety circuitry

3. Write a simple ladder logic program for a task of your own (individual) choosing. Describe the task briefly in words, and then develop a Boolean equation. Other techniques, such as truth tables may be useful. The program should use some/all of the inputs and outputs described in step 1.